Commands and status codes

Instructions

A product query may contain the following requests called instructions in NutShell: actions, input types and post-processing tasks. On command line, they can be set invidually or with --instructions . For logical reasons, some of them are mutually exclusive, like DELETE and EXISTS. Some of them, are implicit; for example, MAKE includes EXISTS and conditionally sets GENERATE.

HTTP request	Command line arg
EXISTS	–exists	Check existence of the product
MAKE	–make, -m	Generate file, if it does not exist (default request)
DELETE	–delete, -d	Delete the product file in cache dir
GENERATE	–generate, -g	Generate file, even if it exists.
–	–copy, -C file	Copy file
–	–move, -m file	Move file
–	–link, -l file	Link file
SHORTCUT	–shortcut	Link file to short directory with original filename
LATEST	–latest, -L	Link file to short directory, $TIMESTAMP replaced with 'LATEST'
INPUTS	–inputlist, -I	Check inputs
TEST	–test	Check existence and permissions of directories and scripts

Some requests specify the product type, for example for make or exist commands:`

Instance type
FILE	–file	Target object is a file
MEMORY	–memory	Target object resides in memory

Note: short forms of command line instructions are available in the Python version only.

Directives

NutShell supports directives, additional instructions that define how a product is computed or what kind of additional outputs like logs should be generated.

A directive should not change the contents of the end product. If it does, it should be applied as a product parameter instead, which appear in filenames as well. Products generated with same parameters but different directives yield an equivalent end result (file).

As with product parameters, directives will be communicated to generator scripts as environment variables.

User may define arbitrarily many directives, for example for selecting an input source from a list of equivalent data centers (mirrors). User should avoid predefined NutShell directives defined below.

Built-in directives

LOG	Save log
STATUS	Also after successful MAKE return the status page (HTML)
NICE	Generate a product with lower CPU priority

Status codes

NutShell recycles some standard HTTP status codes [1] [2] for communicating success or failure on operations. Many of those codes can be also used by the generator scripts in describing errors or other exceptional conditions back to the hosting system, NutShell.

Appicable HTTP codes

Code	Standard Enum Name	NutShell	Comment
102	PROCESSING	x
200	OK	x	Request completed successfully
403	Forbidden	x	Resource exists, but access restricted
404	Not Found	x	File not found (Generator may exist)
405	Method Not Allowed	x
408	Request Timeout	x
409	Conflict		Contradicting parameters
412	Precondition Failed		Required input missing
413	Payload Too Large		Parameters imply expensive computation
415	Unsupported Media Type		Unsupported file format
416	Range Not Satisfiable		Parameter underflow or overflow
425	Too Early		Input data not arrived
500	Internal Server Error		Generator script failed
501	Not Implemented	x	Product generator not found
503	Service Unavailable	x	Busy, come back later

[1]	https://docs.python.org/3/library/http.html

[2]	https://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html